Disk refiners are used in the paper manufacturing industry to prepare the cellulosic fibers of a paper pulp into a desired condition prior to delivery of the pulp to a paper making machine. In operation, a disk refiner is generally considered to exert a species of abrading action upon individual fibers in a pulp mass with the result that the side outermost layers of the individual cigar-shaped fibers are frayed, thereby increasing the surface area of the fiber greatly. The operation of a disk refiner is also generally considered to cause a rapid and frequent flexure over a brief time period of the individual fibers in a pulp mass with the result that the bond between the various concentric lamellae comprising an individual fiber are broken down or delaminated to a controlled, desired extent. The various actions of a disk refiner are accomplished in normal operation without significantly reducing the length or individual strength of the fibers.
The disk members have a working refining surface usually involving a plurality of raised, rib-like projections. In operation, these projections and other portions of the working surface are gradually abraded away, so that it is periodically necessary to shut down a disk refiner and replace the disks used therein.
There are many different types of disks and disk patterns which are well known in the industry. One type is a complete annular disk which is cast as a one piece doughnut shaped member. There are certain advantages in using this type of annular replacement disk in that it is fairly easy to install, and protects the rotor and the support members from wear as a result of the pulp eroding or washing the rotor and stationary mounting walls of the refiner from the abrasive flow of the material from the inner diameter of the refiner to the outer diameter thereof. The major disadvantage of the complete annular ring is the high cost associated therewith.
A second type of refiner disk comprises a plurality of individual segments which cooperatively form an annular ring. The advantage of the segmental disks is the ease of handling, the ability to replace only those segments which are worn and most importantly they are much less expensive to manufacture than the complete one piece annular disk. The disadvantages of the segmental disks are that increased machining time is necessary so that the adjacent disks will mate to form the annular ring and that the segments will fit within the physical constraints placed on them by the mounting surfaces within the refiner.
For purposes of economy, it is common practice to machine only those surfaces of a cast type segmental disk which is necessary to permit proper operation of the complete machine. As such, the disk side edges of are generally left in the "as cast" state and sizable allowances are made for the imperfect casting variations. In general, this has resulted in disks being considerably undersized on the side edges to insure that the disks will fit in the refiner. Therefore, rather sizable channels or spaces are defined between adjacent disks on the stationary mounting walls or rotor within the refiner. When undersized disks are used in the "as cast" edge condition, the abrasive materials flow through the channels between the disks causing severe erosion and washing problems for the stationary walls and rotor of the refiner. The mounting surfaces in some instances, have become so eroded and left in a dangerously weakened state so that a severe safety problem results giving rise to potential injury to the operators. Furthermore, the erosion causes severe problems in the seating of the disk segments when replaced and substantially lessens the life of the replacement disk segments as well as the rotor and walls of the refiner.
The only present known solution to the above problem is to cast the disk segments in a slightly larger form, and machine down the side edges for a custom fitting job. This is extremely expensive and time consuming.
What is desired then, is to provide disk segments which could substantially minimize the adverse effects of erosion of the mounting surfaces of the refiner. It would further be desirable to provide segments which permit ease of installation. It would further be desirable to reuse existing foundry pattern equipment and overcome the above mentioned problems without increasing manufacturing costs.